Don Terrill’s Speed-Talk

What bearing clearance is acceptable when using a 20w50 racing oil... 800 ppm zddp. Dirt track application.

I'm guessing the old .001 for every inch of journal diameter would be OK.

Your input?

Geez... now I feel foolish when the new board feature shows the answer to my question right under this post... I had better get with the program!

thing a beauty, ain't it?

This feature is bad ass. Found many topics that I pulled my hair out to find and they are right there! Thanks Mopar and Mike for making this great!!

FWIW, we just did a dyno test and found 20W-50 cost five horsepower over 10-40. Dynos don't get the oil as hot for as long as does a race, so that's why the stiffer oil is used, but what are the NASCAR guys using these days?

Krooser wrote: ↑Wed Aug 21, 2019 6:22 pm What bearing clearance is acceptable when using a 20w50 racing oil... 800 ppm zddp. Dirt track application.

I'm guessing the old .001 for every inch of journal diameter would be OK.

Your input?

Yes, the .001 per inch of shaft diameter will be just fine.
As others have mentioned, I definitely question the need for 20w-50 oil?!?

PackardV8 wrote: ↑Thu Sep 05, 2019 10:25 pm FWIW, we just did a dyno test and found 20W-50 cost five horsepower over 10-40. Dynos don't get the oil as hot for as long as does a race, so that's why the stiffer oil is used, but what are the NASCAR guys using these days?

Most Nascar teams either use a special blend, formulated by their partner/sponsor, or a high grade shelf racing oil such as Mobil1, Gibbs ect.
0w-30 or 0w-50 Mobil racing is pretty tough to beat for a shelf type oil. IMO

Keep in mind that in regards to proper clearances the need to more clearance at the parting line when things are torqued up for checking.
Even some of the best Rods will pinch in at this area under big loads and just scrape the oil right off the Crank jurnal.

When people scratch there heads over why just one Rod Bearing spun and yet the motor had the needed oil pressure and oil volume, this is one of the main reasons why they had a failure!

This added .0005" to .0008" is put in place by the Bearing itself but can also be done by resizing the rod a certain way .

Warp Speed wrote: ↑Fri Sep 06, 2019 7:44 am

PackardV8 wrote: ↑Thu Sep 05, 2019 10:25 pm FWIW, we just did a dyno test and found 20W-50 cost five horsepower over 10-40. Dynos don't get the oil as hot for as long as does a race, so that's why the stiffer oil is used, but what are the NASCAR guys using these days?

Most Nascar teams either use a special blend, formulated by their partner/sponsor, or a high grade shelf racing oil such as Mobil1, Gibbs ect.
0w-30 or 0w-50 Mobil racing is pretty tough to beat for a shelf type oil. IMO

Once I get my block back I'll know what clearances I have to work with.

This is a SBM originally screwed together in 1993-ish. But I've pretty much started from scratch on the rebuild.

I'd prefer to use a 10-30 but if the need arises I can use the heavier grade.

Gotta be dino oil since I'll be running methanol. I can buy a race oil locally but only in 20-50...at 1/3 the price of most I can buy. If it's a bit loose at least I have an alternative available.